The present application relates to a memory having memory devices.
A system using memories in related art typically uses read only memories (ROMs) that keep information even after power is turned off and random access memories (RAMs) that volatilize information when power is turned off, but can repeatedly perform fast and infinite recording and readout.
These memories in related art are divided into two types of ROMs such as flash memories and RAMs such as dynamic random access memories (DRAMs) and statistic random access memories (SRAMs), and respectively have unique structures.
Recently, memories so-called nonvolatile RAMs such as magnetic random access memories (MRAMs) and ferromagnetic random access memories (FeRAMs) have emerged.
The nonvolatile RAMs have the capability of fast repeated writing and random-access readout equal to that of the RAMs, and do not lose information even after power is turned off.
It is considered that, using the nonvolatile RAMs, the system using both ROMs and RAMs in related art can be simplified and, as a result, its price can be reduced.
In this case, unique information of the system such as a serial number and a network ID and an encryption key for communication etc., which have been placed in the ROMs, are stored in a rewritable RAM area.
Further, as a new nonvolatile RAM, a configuration of spin injection type memory devices in which the direction of magnetization of a ferromagnetic layer of a tunnel magnetic resistance effect device is reversed by spin injection has been proposed (e.g., see JP-A-2003-17782 and NIKKEI ELECTRONICS, Feb. 12, 2001 issue, pp. 164-171).
In the case of the configuration, the nonvolatile RAM has a property of fast repeated writing and random-access readout equal to that of the RAM, and does not lose information even after power is turned off like the above described MRAM.
Therefore, even using the spin injection type memory devices, the system using both ROMs and RAMs in the related art can be simplified as is the case of the above described MRAMs.